I think on some of the stretches gudgeon are present I'm sure i have seen them around inverurie, the sculpin style would imitate these quite well.
I had a large trout take a small trout that I had hooked an a dry.
I've not tried streamers on the Don but on the River Dove I used to do well with them for trout, perch and chub. The perch used to go well over 2lbs and the chub 4lbs. I remember taking a trout home around the pound and a half mark and on gutting the fish it contained 11 minnows.
I think minnows imitations would be a good starting point for the Don.